Apparatus for heating molten metals in a vacuum chamber



Jan. 30, 1962 A. LORENZ APPARATUS FOR HEATING MOLTEN METALS IN A VACUUMCHAMBER Filed Nov. 24, 1958 2 Sheets-Sheet 1 ELECTRICAL POWER SOURCE l6X X DIFFERENTIAL &

ACTUATOR MOTORS MECHANICAL PUMP AMPLIFIER A. LORENZ 3,019,275

APPARATUS FOR HEATING MOLTEN METALS IN A VACUUM CHAMBER Jan. 30, 1962 2Sheets-Sheet 2 Filed Nov. 24, 1958 s sssss Q as sssas FIG 2 UnitedStates Patent '0 3,019,275 APPARATUS FOR HEATING MOLTEN METALS IN AVACUUM CHAMBER Albert Lorenz, Hanan (lVIain), Germany, assignor to W. C.Heraeus G.m.b.H., Hanan (Main), Germany, a corporation of Germany FiledNov. 24, 1958, Ser. No. 775,791 Claims priority, application GermanyNov. 26, 1957 Claims. (Cl. 13-31) The present invention relates to amethod and apparatus for heating metals, and especially steel, for thepurpose of extracting the gases therefrom.

Prior to this invention the gases occluded in molten metals, especiallysteel, were extracted therefrom by passing the metals in a continuousflow through an evacuated chamber. Numerous efforts were then made toimprove such gas extraction by further heating the metals while theextraction process was being carried out. This was done by providingarc-heating or resistance heating means within the closed evacuatedchamber or by making a part of such chamber in the form of a crucibleand surrounding such part with an induction coil. However, these priormethods either do not operate safely and reliably or only veryinefficiently since they do not heat up the entire mass of the metalflowing through the evacuated chamber, but only a small part thereof,that is, either only the surface of the metal or only a negligibleamount in comparison to the volume of the flow.

it is an object of the present invention to provide a new andsurprisingly simple method of heating up the flow of molten metal withinthe evacuated chamber for the purpose of increasing the eificiency ofthe gas extraction considerably over the methods hitherto employed.

A further object of the invention consists in the provision of a newapparatus for heating up the flow of molten metal while passing throughthe evacuated extraction chamber by inducing electric currents withinsuch flow of molten metal in a new and highly improved manner. f

Instead of merely heating up a small portion of the flow of molten metalwithin the evacuated extraction chamber, the present invention providesfor a thorough heating of the entire volume of the flow of metal. Forthis purpose, the present invention utilizes a gas extracting apparatusof the type in which the molten metal is withdrawn from acontainerholding the metal. along one path, then passed through anevacuated extraction chamber, and finally returned to the containeralong a second path which is spaced from the first path. Ac-v cording tothe invention, electric heating currents are then produced by inductionwithin the entire amount of molten metal of such circulation. This isattained by the pro vision of a transformer, the secondary circuit ofwhich is formed by the flow of molten metal and the closed core of whichpasses between the two mentioned paths of the flow of metal and carriesa primary induction coil which is energized by an alternating current ofa standard frequency. As soonas the molten metal flows over from thefirst or intake path into the second or return path, the secondarycircuit of the transformer will be closed and itthereby reacts upon thecurrent flowing through the primary coil. The beginning of this reactionmay be utilized for indicating the beginning of the continuousgas-extraction process, and the strength of this reaction upon theprimary current produced by a stronger or weaker flow of molten metalmay also be utilized for effecting and controlling the gas-extractionprocess.

These and further objects, features, and advantages of the presentinvention will become more apparant from the following detaileddescription thereof, particularly when read with reference to theaccompanying drawings, in which- FIGURE 1 shows diagrammatically andpartly in section one preferred embodiment of the present invention;while FIGURE 2 shows a cross section taken along line A--A of FIGURE 1.

Referring to the drawings, the container or ladle 1 holds the moltenmetal 2 from which the gases occluded therein are to be expelled bymeans of the gas-extraction apparatus 3 which is partly immersed fromabove into the metal bath. This apparatus consists of an extractionchamber 5 which is continuously evacuated through a pipe 4 leading to apump and control valve unit 4. Chamber 5 has a pair of pipes 6 and 7extending vertically downward therefrom and into the bath of moltenmetal 2 at a considerable distance from each other. By injecting a gasthrough a pipe 8 into inlet pipe 6, a continuous flow of metal will bestarted and maintained, rising from the bath in ladle 1 through pipe 6into chamber 5, and then flowing through this chamber toward the returnpipe 7 and through the latter back into the bath in ladle 1. The gasbubbles then rising in pipe 6 will take along the metal and convey itupwardly into the actual extraction chamber 5. The gas supply may beregulated by a suitable valve mechanism 8. A suitable hopper 9 or thelike containing alloying constituents is also connected to chamber 5 forsupplying these materials to the fiow of metal passing through thechamber. Hopper 9 is likewise adapted to be sealed 7 hermetically towardthe outside, and it is provided with suitable means, as diagrammaticallyindicated at 10 in FIGURE 1, for controlling the supply of thesealloying constituents into chamber 5.

The gas extracting apparatus as such is enclosed by a metallic covering11 which is adapted to take up the outside pressure acting upon theapparatus, and it is provided at the inside with a lining of refractorymaterial. Covering 11 also extends around the intake and return pipes 6and 7 to a point closely above the surface of-the bath of molten metal 2in ladle 1. Thus, the pipe portions extending into the bath of metalonly consist of refractory material and are carried by the metalcovering 11.

Interposed between the inlet and return pipes 6 and 7 is a practicallyclosed iron transformer core 12 which also carries a primary coil 13which is supplied with an alternating current of a standard linefrequency. By means of this transformer core 12 a very strongalternating current will be induced in the molten metal flowing from thebath 2 in ladle 1 through inlet pipe 6, chamber 5, and return pipe 7back into bath 2. The path of the current in the metal bath 2 isindicated in FIGURE 1 by the dotted line 14. Since the cross-sectionalarea of the bath itself is very large, the resistance incurred by thecurrent passing therethrough is very small. As the metal covering 11 ofthe apparatus does not extend entirely to the surface of the metal bath2, there is no danger of a short circuit of the induced current due tosuch covering. Within the extraction chamber 5, however, the moltenmetal flows from inlet pipe 6 to return pipe 7, and during such passageit strongly sprays and spatters. The cross-sectional area of the moltenmetal which is present at this passage at all times is thereforerelatively small, with the result that the electric resistance and theheating effect produced within the metal in the chamber itself is veryhigh.

The heat is therefore generated primarily within the upper part of theheated path 265--72 of the molten metal. This, however, is the placewhere only a small amount of the molten metal is separated from thegreat mass of the bath 2 and Where it is therefore to be expected morethan at any other place that the molten metal will cool off or may evensolidify. On the other hand, this is also the point Where relativelycold alloying constituents may be added from the hopper 9 by its feedcontrol device 10. It is therefore necessary that the heat required formelting or dissolving these additions will also be supplied at thispoint.

The most important requirement for carrying out the method according tothe invention is the fact that the molten metal passing through theapparatus always has to form a closed electric circuit. Obviously thecirculation of the molten metal by means of an added gas as previouslydescribed may also be attained by different means, for example, bycentrifugal conveying means of the type described in the inventorsprevious United States Letters Patent No. 2,893,860, or the like.

The method according to the present invention has, however, certainother very important advantages. As already stated, the uninterruptedcirculation of the molten metal forms the secondary circuit of atransformer. This secondary circuit is closed after the apparatus hasbeen evacuated and the conveying gas has been introduced through pipe 8and at the very moment when the molten metal flows over from pipe 6 topipe 7. After the electric current has been switched on to operate thetransformer 12, 13, this moment may be easily determined by an ammeter15. This serves as a clear indication of the fact that the continuousgas extraction process has been started. The ammeter will also indicateany interferences in the normal operation of the apparatus, for example,an interruption in the continuous flow of metal, and the like.

The strength of the alternating line current which may be about 100 kw.or more may, however, to a certain extent also furnish an indication ofthe volume of the flow of metal through vacuum chamber 5. The amperageindicated by ammeter may therefore indicate the volume and velocity ofthe flow and it may also be used for controlling the flow, for example,by an adjustment of the position and elevation of the gas extractingapparatus relative to the bath of molten metal 2 vertical positioningdevice indicated generally at 16, by an adjustment of the amount ofconveying gas supplied through pipe 8, or by an adjustment of the outputof the evacuating pump and control valve unit 4 which is connected topipe 4, or by similar means. Such adjustments may also be producedautomatically by suitable means known in the art which operate inresponse to the indication of ammeter 15 and the changes in the strengthof the primary current.

From the above description, it will be clearly apparent that the newmethod of expelling the gases occluded in a molten metal, andparticularly in steel, is very simple and highly efficient, and requiresonly a very simple and relatively inexpensive apparatus.

Although my invention has been illustrated and described with referenceto the preferred embodiments thereof, I wish to have it understood thatit is in no Way limited to the details of such embodiments, but iscapable of numerous modifications within the scope of the appendedclaims.

Having thus fully disclosed my invention, What I claim 1. An apparatusfor heating up molten metals comprising a container for holding a moltenmetal, a vacuum chamber having an inlet conduit and an outlet conduitthereon and extending downwardly therefrom, means for suspending saidvacuum chamber above said container and for raising and lowering thesame relative to said container and for immersing: the free ends of saidconduits into said molten metal, means for evacuating said chamber andthe unimmersed parts of said conduits above the surface of said moltenmetal Within said container, means for conveying the molten metalthrough said inlet conduit into said vacuum chamber, and means forinducing a strong electric current in the entire volume of molten metalcirculating through said conduits and said vacuum chamber for increasingthe temperature thereof.

2. An apparatus as defined in claim 1, further comprising means foradding other materials under a vacuum to the molten metal within saidvacuum chamber for alloying said molten metal with said added materialsby the heat of said metal.

3. An apparatus as defined in claim 1, wherein said evacuating means areconstructed and arranged to operate continuously to withdraw the gasesliberated from said molten metal within said vacuum chamber.

4. An apparatus as defined in claim 1, wherein said conveying meanscomprise means for injecting a gas into said inlet conduit adapted totake along the molten metal through said inlet conduit into said vacuumchamber.

5. An apparatus as defined in claim 1, wherein said induction meanscomprise a transformer having a substantially closed iron core and aprimary induction coil mounted on said iron core and adapted to beconnected to a source of alternating current, said molten metalcirculating in a continuous flow from said container through said inletconduit, said vacuum chamber and said outlet conduit back to saidcontainer serving as a secondary circuit of said transformer.

6. An apparatus as defined in claim 5, wherein said substantially closediron core of said transformer extends between said two conduits, andmeans for indicating the reaction upon the induction current within saidprimary coil for determining the beginning of a continuous process ofextracting gases from said molten metal within said vacuum chamber.

7. An apparatus as defined in claim 6, further comprising means wherebysaid reaction upon the primary induction current is utilized forcontrolling the operation of the gas extraction process.

8. An apparatus as defined in claim 6, wherein said control meanscomprise means for adjusting the elevation of said vacuum chamberrelative to the surface of the molten metal within said container.

9. An apparatus as defined in claim 6, wherein said control meanscomprise means for adjusting the operation and output of said evacuatingmeans.

10. An apparatus as defined in claim 6, wherein said conveying meanscomprise means for injecting a gas into said inlet conduit constructedand arranged to take along the molten metal through said inlet conduitinto said vacuum chamber, said control means comprising means forcontrolling the amount of gas injected into said inlet conduit by saidinjecting means.

References Cited in the file of this patent UNITED STATES PATENTS761,920 Schneider June 7, 1904 2,587,793 Waldron Mar. 4, 1952 2,848,317Coupette et al. Aug. 19, 1958 2,859,262 Harders et al. Nov. 4, 1958

